LocalDistributedExecutor: Execute multiple TaskManagers in one JVM

Fix for this issue: https://github.com/dimalabs/ozone/issues/86

The LocalDistributedExecutor simulates a Nephele-Cluster with multiple TaskManagers in one JVM. Data between the TMs is transferred using the OS network stack, not through memory. This is important to find bugs in the network stack.

It would be great to integrate the LDE with `TestBase` and `TestBase2`. I already started with this, but I had some errors.

(this is my second LDE PR, the first one (https://github.com/stratosphere/stratosphere/pull/130) had some issues)